Septic Tank Size Calculator
Tank capacity for your household.
Enter your values
Enter the bedrooms you are working with.
Enter the occupants you are working with.
Enter the water use per person in gal/day.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Recommended tank size
- 1,000 gallons
- Daily wastewater flow
- 280 gallons
- Minimum by bedroom count
- 1,000 gallons
- Retention time target
- 48 hours minimum
- Pump-out interval estimate
- 0.5 years
Quick answer
Most codes require at least 1000 gallons for a three bedroom home, rising with bedroom count and daily flow.
At a glance
| What it does | Tank capacity for your household. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Bedrooms, Occupants, Water use per person |
| Main output | Recommended tank size |
| Cost | Free — no sign-up, no download |
How to use the Septic Tank Size Calculator
- 1Enter the number of bedrooms — most codes size on this.
- 2Enter actual occupants and water use.
- 3Use the larger of the two figures.
Inputs explained
- Bedrooms
- Enter the bedrooms you are working with.
- Occupants
- Enter the occupants you are working with.
- Water use per person(gal/day)
- Enter the water use per person in gal/day.
Worked example
Using the values the calculator loads with:
Inputs
- Bedrooms3
- Occupants4
- Water use per person70 gal/day
Results
- Recommended tank size1,000 gallons
- Daily wastewater flow280 gallons
- Minimum by bedroom count1,000 gallons
- Retention time target48 hours minimum
- Pump-out interval estimate0.5 years
Frequently asked questions
How often should I pump?
Every 3–5 years for a typical family of four.
Does a garbage disposal matter?
Yes — it adds solids, so consider a larger tank.
What do I need to enter into the Septic Tank Size Calculator?
Just 3 values: bedrooms, occupants, water use per person. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Septic Tank Size Calculator work out the answer?
Most codes require at least 1000 gallons for a three bedroom home, rising with bedroom count and daily flow. The working is shown step by step so you can verify the result by hand.
Is the Septic Tank Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.